Device and a method for stabilising a web or a filament of ferromagnetic material moving in one direction

ABSTRACT

A device and a method for stabilising a metallic object of magnetic material. The metallic object is transported along a transportation path or plane. The plane includes a transportation direction and is parallel to the longitudinal direction of the object therein. A sensor is arranged to sense the valve of a parameter depending on the position of the object with respect to the plane. An electromagnetic actuator is arranged to apply a magnetic force to the object in respone to the sensed position. The magnetic force has a force component directed transversely to the transportation direction and transversely to the plane.

BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention refers to a device for stabilising an elongatedmetallic object of magnetic material, the metallic object being intendedto be transported along a transportation path located in a plane, whichincludes a transportation direction and is substantially parallel to thelongitudinal direction of the object in said path. Moreover, theinvention refers to a method for stabilising an elongated metallicobject of magnetic material, wherein the metallic object is transportedalong a transportation path located in a plane, which includes atransportation direction and is substantially parallel to thelongitudinal direction of the object in said path.

In different industries, there is a need to transport continuouslyelongated metallic objects, such as metallic strips or wires in rollingmills, in different metal coating applications, such as continuousgalvanising of steel strips or steel wires, continuous casting,extrusion etc. During such continuous transportation, a portion of theobject is extended in a plane and transported in a longitudinaldirection of the object in said plane. For efficiency reasons, it isimportant to obtain a high transportation speed. However, a hightransportation speed can result in problems to keep the object stable inthe plane, i.e. to maintain the position of the object with respect tothe plane and prevent transversal deflections of the object.

U.S. Pat. No. 4,655,166 discloses an apparatus for preventingoscillations of a running strip in connection with galvanising of thestrip. The apparatus comprises permanent magnet units arranged in thevicinity of the two opposite side edges of the running strip. Detectorsare provided to detect the gap between the side edges and the respectivemagnet unit. In order to maintain the size of the gap at determinedlevel, control motors are provided to adjust the position of the magnetunits in response to the detected gap.

U.S. Pat. No. 3,661,116 discloses a similar device for stabilising ametal strip. An electromagnet extends along a path in such a way thatthe poles are arranged outside and in the vicinity of a respective sideedge of the strip.

SUMMARY OF THE INVENTION

The object of the invention is to improve the stabilisation of ametallic object during transportation, in particular duringtransportation at a high transportation speed.

This object is obtained by the device initially defined, which ischaracterised in that it includes a sensor arranged to sense the valueof parameter depending on the position of the object with respect to theplane and a substantially stationary electromagnetic actuator arrangedto apply a magnetic force to the object in response to the sensedposition, wherein the magnetic force includes at least a force componentdirected transversely to the transportation direction and transverselyto the plane.

By such device it is possible to obtain a proper positioning of theobject with respect to the plane so that the object runs along the planein a stable manner. Moreover, since the actuator enables correction ofthe transversal position of the object with respect to the plane by amagnetic force, no contacting of the object is required.

According to an embodiment of the invention, the actuator includes atleast a first actuating member arranged on a first side of the plane andat a determined distance from the plane. Furthermore, the actuator mayalso include a second actuating member arranged on a second side of theplane and at a determined distance from the plane. Thus, the actuatordefines said plane between the first actuating member and the secondactuating member. Preferably, the first actuating member may be arrangedat the same distance from the plane as the second actuating member buton the opposite side thereof.

According to a further embodiment of the invention the first actuatingmember is positioned essentially exactly opposite to the secondactuating member. Preferably, the first actuating member may besubstantially identical to the second actuating member. By such asymmetric arrangement of the actuating members with respect to theplane, both the sensing function and the control function may beachieved in an easy manner.

According to a further embodiment of the invention, the actuator isarranged to increase the magnetic force of one of the actuating memberswhen the position of the object deviates from said plane.

According to a further embodiment of the invention, said actuatingmember includes a magnetic flux carrier forming a magnetic flux circuitwith a part of the object. Said magnetic flux carrier may have a firstend arranged to be located in the proximity of the object and a secondend arranged to be located in the proximity of the object, wherein saidpart of the object extends substantially between the first end and thesecond end. Such a magnetic flux carrier may be made of any suitablemagnetic material, such iron plates, magnetic powder etc., and may beshaped as loop extending between the first end and the second end, saidends forming magnetic poles of said actuating member.

According to a further embodiment of the invention, the device includesa control unit arranged to apply voltage pulses to the actuator inresponse to said sensed value, thereby generating said magnetic force.Said actuating member may include a winding connected to said controlunit, wherein the control unit is arranged to apply said voltage pulsesto the winding to induce a magnetic flux in the magnetic flux carrier.Preferably, the control unit is arranged to apply said voltage pulseshaving a substantially constant amplitude, and thereby to vary themagnetic force by varying the length of the voltage pulses.

According to a further embodiment of the invention the sensor isarranged to sense the level of the electric current through the winding.Such as sensor is not in contact with the object and the sensingfunction will not influence the position of the object. Moreover, bysuch a sensor the winding may involve both the actuating function andthe sensing function.

According to a further embodiment of the invention, the control unit isarranged to increase the magnetic force applied by said actuating memberwhen the level of the electric current through the corresponding windingincreases. Thereby, the sensor may include a first sensor memberarranged to sense the level of the current through the first actuatingmember and a second sensor member arranged to sense the level of thecurrent through the second current member, wherein the control unit isarrange to compare the current level through the first actuating memberwith the current level through the second actuating member and toincrease the length of the voltage pulses through the winding of theactuating member having the highest current level.

According to a further embodiment of the invention, the control unitincludes a so-called DC-chopper.

The object is also obtained by the method initially defined, which ischaracterised by the steps of:

-   sensing the value of parameter depending on the position of the    object with respect to the plane, and-   applying a magnetic force to the object in response to the sensed    value, wherein the magnetic force includes at least a force    component, acting on the object and directed transversely to the    transportation direction and transversely to the plane.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be explained in more detail withreference to different embodiments, disclosed by way of example only,and with reference to the figures attached.

FIG. 1 discloses schematically a device for stabilising a metallicobject according to the invention.

FIG. 2 is a diagram disclosing the current through a winding of arespective actuating member in response to voltage pulses.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

FIG. 1 discloses a device for stabilising a running elongated metallicobject 1 of magnetic material. In the embodiment disclosed the object isa metal strip 1. It is to be noted, however, that the invention also isapplicable to other elongated objects such as different bands, wires,pipes etc. In the embodiment disclosed the metal strip 1 is transportedor substantially continuously moved from a first roll 2 to a second roll3 along a transportation path located in a plane x. In FIG. 1 the planex is substantially vertical. However, the plane x and the transportationpath may extend in other directions than a vertical one, for instance ina horizontal direction.

It should be noted that the rolls 2, 3 are schematically indicated tosubstantiate the transportation path. Such a transportation path canform a part of many different industrial processes, for instancegalvanising of steel strips, rolling mill processes, extrusion etc.

The device according to the invention includes a sensor arranged tosense the value of a parameter depending on the position of the metalstrip 1 with respect to the plane x, or in other words depending on thedistances of the metal strip 1 from the plane x. The sensor includes afirst sensor member 5 and a second sensor member 6. Each sensor r 5, 6is arranged to sense a current level. The sensor members 5, 6 are to bedescribed more closely below.

Furthermore, the device includes a substantially stationaryelectromagnetic actuator arranged to apply a magnetic force to the metalstrip 1 in response to said sensed value. The electromagnetic actuatorincludes a first substantial stationary actuating member 7, which isarranged on a first side of the plane x and at a determined distancefrom the plane x, and thus from the running metal strip 1. The actuatoralso includes a second substantial stationary actuating member 8, whichis arranged on a second side of the plane x and at a determined distancefrom the plane x, and thus from the metal strip 1. Each actuating member7, 8 includes a magnetic flux carrier in the form of a core 91, 91″ ofiron or any suitable magnetic material, such as iron plates, magneticiron powder etc. Each core 9′, 9″ is formed as a loop extending betweena first end and a second end, wherein said ends form two magnetic polesof the respective actuating meaner 7, 8. Furthermore, each actuatingmember 7, 8 includes an electric winding 11′, 11″ which is wound arounda respective core 9′, 9″. Consequently, a voltage applied to the winding11′, 11″ will induce a magnetic flux in the core 9′, 9″ and asubstantially closed magnetic flux circuit is obtained by the core 9′,9′ and a part of the metal strip 1, which part extends between the twomagnetic holes of the respective core 9′, 9″.

In the embodiment disclosed, the first actuating member 7 is positionedsubstantially exactly opposite to the second actuating member 8.Moreover, the first actuating member 7 is substantially identical to thesecond actuating member 8, and the two actuating members 7, 8 arepositioned at the same distance from the plane x and thus from the metalstrip 1, when the metal strip 1 is located in the intendedtransportation path. Thus, the plane x font a middle plane x between theactuating 7, 8.

The device according to the invention also includes a control unit 13arranged to apply voltage pulses to the windings 11′, 11″ of the firstactuating member 7 and the second actuating member 8, respectively, inresponse to the values sensed by the first sensor member 5 and thesecond sensor member 6, respectively.

The control unit 13 form a so-called DC-chopper and includes a linerectifier 14 to be supplied with a three-phase AC-voltage. In parallelto the rectifier 14 a capacitance 15 is provided. The windings 11′, 11′are also connected in parallel to the rectifier 14 via the respectivesensor member 5, 6 and a switching device represented by ananti-parallel diode 16′, 16″ and a one-way current switch 17′, 17″ (thefilled arrows indicate the current direction). Furthermore, the controlunit 13 includes a processor 18 which is connected to the first sensormember 5, the second sensor member 6, the switch 17′ and the switch 17″.

The first sensor member 5 and the second sensor member 6 are arranged tosense the current level through the respective winding 11′ and 11″. Theprocessor 18 is connected to the sensor members 5 and 6 and arranged toreceive the sensed level from the sensor members 5, 6. Furthermore, theprocessor 18 is connected to the switches 17′ and 17″ and arranged toinitiating switching of the switches 17′, 17″ between an open state, seeswitch 17′, and a closed state, see switch 17″. By closing the switch17′, 17″ a voltage will be applied to the respective winding 11′, 11″.Consequently, the processor 18 will apply voltage pulses V to theactuating members 7, 8 of a certain length T, see FIG. 2. The voltagepulses induces a current in the respective winding 11′, 11″, and bymeans of the sensor members 5, 6 the current level through the windings11′, 11″ is measured. The current level through the windings 11′, 11″depends on the magnetic inductance of the respective magnetic fluxcircuit. If the distance between the metal strip 1 and the ends of thecore 9′, 9″ increases, the magnetic inductance of the magnetic fluxcircuit decreases, which means that the current through the winding 11′,11′″ will increase since the magnetic inductance of the magnetic fluxcircuit is reciprocally proportional to the current through the winding11′, 11′″.

FIG. 2 indicates the voltage pulses V and the current I with respect tothe windings 11′ and 11″. In the winding 11′ the current I is at ahigher level for the voltage pulse V₁, which means that the metal strip1 is positioned closer to the second actuating member 8 than the firstactuating member 7. To compensate for this, the second voltage pulse V₂is prolonged so that the first actuating member 7 will apply anattracting magnetic force on the metal strip 1 during a longer period oftime than the second actuating member 8, and consequently, the metalstrip 1 will be forced to the position of the middle plane

The present invention is not limited to the embodiments disclosed by maybe varied and modified within the scope of the following claims.

1. A device for stabilizing an elongated metallic object of magneticmaterial, the metallic object being intended to be transported along atransportation path located in a plane (x), which includes atransportation direction and is substantially parallel to thelongitudinal direction of the object in said path, wherein the devicecomprises a substantially stationary electromagnetic actuator arrangedto apply a magnetic force to the object and includes at least a firstactuating member which includes a winding and is arranged on a firstside of the plane and at a selected distance from the plane, wherein thedevice includes a sensor arranged to sense the level of the electriccurrent through the winding depending on the position of the object withrespect to the plane, wherein the substantially stationaryelectromagnetic actuator is arranged to apply the magnetic force to theobject in response to the sensed value, and wherein the magnetic forceincludes at least a force component, acting on the object and directedtransversely to the transportation direction and transversely to theplane.
 2. (canceled)
 3. (canceled)
 4. A device according to claim 1,wherein the first actuating member is positioned essentially exactlyopposite to the second actuating member.
 5. A device according to claim1, the first actuating member is substantially identical to the secondactuating member.
 6. A device according to claim 1, wherein the actuatoris arranged to increase the magnetic force of one of the actuatingmembers when the position of the object deviates from said plane.
 7. Adevice according to claim 1, wherein said actuating member includes amagnetic flux carrier forming a magnetic flux circuit with a part of theobject.
 8. A device according to claim 7, wherein said magnetic fluxcarrier has a first end arranged to be located in the proximity of theobject and a second end arranged to be located in the proximity of theobject, wherein said part of the object extends substantially betweenthe first end and the second end.
 9. A device according to claim 1,wherein the device includes a control unit arranged to apply voltagepulses to the actuator in response to said sensed value, therebygenerating said magnetic force.
 10. A device according to claim 9,wherein said actuating member includes a winding connected to saidcontrol unit, wherein the control unit is arranged to apply said voltagepulses to the winding.
 11. A device according to claim 10, wherein thecontrol unit is arranged to apply said voltage pulses having asubstantially constant amplitude.
 12. A device according to claim 10,wherein the control unit is arranged to vary the magnetic force byvarying the length of the voltage pulses.
 13. (canceled)
 14. A deviceaccording to claim 10, wherein the control unit is arranged to increasethe magnetic force applied by said actuating member when the level ofthe current through the corresponding winding increases.
 15. A deviceaccording to claim 14, wherein the sensor includes a first sensor memberarranged to sense the level of the current through the first actuatingmember and a second sensor member arranged to sense the level of thecurrent through the second actuating member, wherein the control unit isarranged to compare the current level through the first actuating memberwith the current level through the second actuating member and toincrease the length of the voltage pulses through the winding of theactuating member having the highest current level.
 16. A deviceaccording to claim 9, wherein said control unit includes a so-calledDC-chopper.
 17. A method for stabilising an elongated metallic object ofmagnetic material, with a substantially stationary electromagneticactuator arranged to apply a magnetic force to the object wherein themetallic object is transported along a transportation path located in aplane, which includes a transportation direction and is substantiallyparallel to the longitudinal direction of the object in said path, andwherein the actuator includes at least a first actuating member whichincludes a winding and is arranged on a first side of the plane and at aselected distance from the plane and a second actuating member whichincludes a winding arranged on a second side of the plane and at aselected distance from the plane, comprising the steps of: sensing thelevel of the electric current through said winding, the level dependingon the position of the object with respect to the planed and applyingthe magnetic force to the object in response to the sensed value,wherein the magnetic force includes at least a force component, actingon the object and directed transversely to the transportation directionand transversely to the plane.
 18. A device according to claim 10,wherein the control unit is arranged to apply said voltage pulses havinga substantially constant amplitude.